Eleni Naziri

Industrial Glycerol as a Supplementary Carbon Source in the Production of β-Carotene by Blakeslea trispora

The dynamics of industrial types of glycerol as a supplementary carbon source to glucose for beta-carotene production by Blakeslea trispora was investigated in batch cultures. The growth kinetics, cellular lipid accumulation-degradation, substrate assimilation, and beta-carotene production were clearly dependent on the level of addition of pure glycerol. The highest beta-carotene production (15.0 mg/g of dry biomass) was obtained at an initial glycerol concentration of 60.0 g/L. Substitution of pure glycerol by the nonpurified soap byproduct did not inhibit cell growth. Conversely, partial purification of the biodiesel byproduct by removing methanol and fatty acids was unavoidable for cell growth. Both types of industrial glycerol stimulated beta-carotene synthesis more than 10 (soap byproduct) and 8 times (biodiesel byproduct) compared to control medium. The maximum beta-carotene contents were 10 and 8 mg/g of dry biomass, respectively, and its relative content in the carotenoid fraction was 86-88%.

Squalene versus Ergosterol Formation Using Saccharomyces cerevisiae: Combined Effect of Oxygen Supply, Inoculum Size, and Fermentation Time on Yield and Selectivity of the Bioprocess

The dynamics of two wild type strains of Saccharomyces cerevisiae (BY4741 and EGY48) that vary in the ability to produce sterols were compared in batch cultures under different aeration conditions. Poor supply of oxygen enhanced selectivity of the bioprocess in favor of squalene formation. Optimization of inoculum size and fermentation time arranged according to a central composite statistical design revealed significant differences between the strains in terms of yield and productivity. Experimental verification showed that an optimized bioprocess under semianaerobic conditions is competitive with regard to those reported in the literature. Maximum squalene yield and productivity were, respectively, 2967.6 +/- 118.7 microg/L of culture medium and 104 +/- 4.2 microg/Lh for BY4741 and 3129 +/- 109.5 microg/L of culture medium and 155.9 +/- 5.5 microg/Lh for EGY48. The prospect of developing high-purity squalene preparations that meet food safety regulation demands is expected to attract the interest of the food industry.

Enhanced squalene production by wild-type Saccharomyces cerevisiae strains using safe chemical means.

Interest is increasing in establishing renewable sources for squalene, a functional lipid, as the conventional ones are limited. In the present study, squalene production was achieved in a wild-type laboratory Saccharomyces cerevisiae strain by two safe chemical means using terbinafine (0.05-0.55 mM) and methyl jasmonate (MJ) (0-1.00 mM). Bioprocess kinetics optimized by response surface methodology and monitored by high-performance liquid chromatography revealed a clear dependence of growth and squalene content (SQC) and yield (SQY) on the above regulators. Maximum SQC (10.02±0.53 mg/g dry biomass) and SQY (20.70±1.00 mg/L) were achieved using 0.442 mM terbinafine plus 0.044 mM MJ after 28 h and 0.300 mM terbinafine after 30 h, respectively. A 10-fold increase in SQY was achieved in comparison to that in the absence of regulator. The ruggedness of optimum conditions for SQY was verified for five industrial strains. The cellular lipid fraction (∼12% of dry biomass) was rich in squalene (12-13%). Results are encouraging toward bioprocess scale up.